A number of practical applications make it necessary or desirable to measure or adjust the tension in a filament. For example, the drive belts of an automobile engine must be adjusted to the proper tension to prevent premature wear and failure of the accessories which the belts drive and to prevent the belt from slipping or coming off of the pulleys or sprockets which support the belt. Similarly, the proper fabrication of a stranded rope or cable requires that the tension of the strands be properly controlled when those strands are wound together. Weaving fabrics requires a control over the tension in the individual threads. The tension in suspended filaments, such as electrical power lines, chair lift haul cables, well drilling tool lifting cables, and passenger elevator lift cables must also be checked periodically to determine the tension for safety and other reasons. The tension in the belts and cords which are employed in automobile tires and in drive belts must also be controlled when the tires are manufactured. In short, a myriad of different situations require the tension of a filament to be measured and determined, and most of these situations require the tension to be measured without gaining access to the ends of the filament and while the filament is experiencing tension.
A variety of measurement devices are available for measuring the tension in contained or endless filaments. One of the most common types of tension measuring devices operates on a geometric principal where the filament is deflected laterally between a pair of stationary reference points by a laterally deflecting element which is located midway between the stationary reference points. The force on the laterally deflecting element is created by the tension in the filament. The amount of force on the laterally deflecting element is measured. Because of the geometric relationship of the stationary reference points and the laterally deflecting element, the measured force is trigonometrically related to tension in the cable.
Despite this well known relationship, previous tension measurement devices do not account for variation in filament widths and result in inaccurate tension measurements in many situations. Other previous devices attempt to determine the tension measurements using analog measurements of mechanical devices such as occur from spring deflection. Such analog measurements and calculations can not be precise enough to supply accurate measurements. In addition, many such prior devices require manual adjustment and setup, which is difficult or impossible for a non-skilled operator to accomplish with sufficient facility to obtain accurate tension measurements. Furthermore, some prior tension measurement devices require that the operator establish certain initial conditions, such as a predetermined amount of filament deflection, before the measurement can be accomplished. These initial conditions are intended to avoid having to account for many of the practical variables which may influence the tension measurement, such as temperature, friction and the angle or amount of filament deflection. Lastly, although the geometric and trigonometric relationships used to measure tension are sound from a theoretical standpoint, problems occur because of aberrant influences. Examples of aberrant influences include unexpected and possibly unexplained force measurements. These aberrations will also influence tension calculation, because the tension is directly related to the force measurement. All of these factors contribute to prior tension measured devices having reduced accuracy and difficulty of operation.
It is with respect to these general considerations, and other more specific background information, that the present invention has evolved.